Level luffing jib crane



Oct. 9, 1945. KAY

LEVEL LUI'TFING J 13 CRANE Filed March 15, 1944- 2 Sheets-Sheet 1 "0.19, 1945 7 4 HQAy' v 2,386,475

LEVEL LUFFING J IB CRANE Filed March 15, 1944 2 sheets sheet 2 and Patented Oct. 9, 1945 We'llman Smith Owen Engineering Corporation ..Limited, London, England, a company of Great Britain Application Mareh 15, 1944, Serial No. 526,577

In Great Britain March 15, 1943 7 12 Claims.

This invention relates to level lufiing jib cranes and has for itsmain object the provision of an improved construction which shall have the generally recognizedcharacteristics of such a crane while being capable of operation at high; speed with complete safety. j n

The characteristics referred to are, briefly, (1') horizontal movement of, the loadhook when the jib is luifed and (2),,a balanced jib. A desirable additional feature, not found in all level lufling cranes but possible to provide in those according to this inventi n, is (3) substantia ly constant horizontal velocity of the load hook. during luffing of the lib, .The horizontal movement of the hookshould preferably bedue to operation of the luffing gear only, independently of the hoist gear, so that -bothluffing and hoisting may be effected se h rw n d re t I inventicm consists in a level lufling jib cran ha in bal nge Ji t e o s a v of which movesin a substantial]yherizontal path during thelufling-of the jib and in which the latter is supported from the frame of the crane by links orthe equivalent so disposed and dimensioned that the end of the jib remote from ;the load is constrained to move in a substantially vertical path. v n

In orderthat the inve tion maybe clearly understood, there will now be described some practical examples of the improved crane construction and the way in which it has been developed panying diagrammatic drawings.

In e aw 1 u r Figs. 1 to flu, inclusive, are line diagrams illustheoretically, reference being made tothe accomtr t ns ,stas i he, de en of th l nka arrangement constituting a main feature of this ven i n. g.

F -1. 1 adi gr mm Side v tionof v form of crane embodying a practical example of this linkage arrangement, the centre of gravity of the jib being at the centre of length of the tter. 7. ss m ar e of a her rane according to the invention in which a different location of the centre of gravity of the jib. has necessitated an alteration in the reeving of the ropes,

Fig. 7 is a similar view of a third form of crane having two separate load hooks which are of diifeirent lqadeariyingcapacities and located at difierent distances fromthe centre of gravity heJib-,:

In each of the -Figs.; to 7 only the parts essentialto the cleaiyunder standing of the present invention; have been indicated, the main members of the jib being shown in heavy lines and the nain members of the frame by double lines. Manyof the bracing members, and other known constructional details, including means permit ting of slewing the crane or traversing it along rails when-desired, have not been illustrated as their arrangement'or construction will be obvious to those skilled in the art.

The manner in which the cranes according to this invention are adapted to operate can best beexp'lained by reference to the diagrams of Figs. 1 to 4. I 1

As a first step and considering Fig. 1, assume that a pivoted jib A, B mounted on a crane framenot shown) has rigidly afiixed thereto at the pivotal point C the upper endof a downwardly extending arm D (equal in length to the tail portion B of the jib extending beyond the pivot '0) having its lower end pivoted at E to the forward end of a thrust link F'disposed substantially parallel with the tail portion B. If the rear end of the thrust link F 'be located (as shown) vertically beneath the end of the tail portion B and there pivoted, at G, to the upper end of a radial link H which extends downwardly and forwardly to a fixed pivot I on the crane frame (not shown) vertically beneath the pivotal point C of the jib and is of the same length as the arm D secured to the jib, any angular movement imparted to any member of the systemisee the'chain-dotted lines) will be exactly repeated by the remaining members of the system with the excep'tionof the thrust link F which will move substantially in the direction of its length. n addition, the reduction in the distance between the rear ends of the radial link H and jib tail-portion B will bear a definite ratio to the lift of the upper extremity of the jib head-portion A. I Furthermore, the said rear ends will always be contained in a vertical plane. j

Proceeding from the foregoing and referring now toF'ig. 2 let the radial link H be removed from the thrust link F and the pivot G at the rear end ,of this latter be mounted on the crane frame; Then re-attach the radial link H pivotally to the jib A, B at its pivot point C (which is not now mounted on the crane frame and is free to move) and pivot its upper end on a fixed point J on the frame (not shown) vertically above the rear ends of the thrust link F and jib tail-portion B. Angular motion of the radial link H about point J now causes the upper end of the arm D to moverearwards where before a similar move,- ment forwards of its lower end. would have been produced (see chain-dotted lines in Fig. 2) However, "the reduction inthe distance between the rear ends of the thrust link Fand tail-portion B still bears a definite ratio to the lift of the upper end of the jib head-portion A, the numerical value of this ratio depending on the relation between the lengths of the head and tail portions, A and B, respectively, of the jib. It should be noted, however, that the rear end of the tailportion B is now always contained in the same vertical plane.

the last arrangement are each extended beyond the pivots E and C respectively (see Fig. 3) they meet at K vertically beneath a point L on the jib head-portion A which is horizontally opposite to the fixed pivot J for the radial link H, the meeting point K also being located horizontally opposite to the rear end of the jib tail portion B. This applies whatever the position of the jib (see the alternative positionof the parts shown in chain-dotted lines in Fig. 3) so that it follows that the point L of the head-portion A moves in a horizontal path.

It will now be seen that if it be arranged for the centre of gravity of the jib A, B to be located at the point L of the head-portion A the jib will be in balance for any position of this point along its horizontal path of travel and, further, that if hoisting rope pulls acting vertically on the jib at its forward and rearward ends as indicated by the arrows M and N in Fig. 3 bearranged to have an equal moment about the said point they also will be balanced. Should the. centre of gravity L be at the centre of length of the jib A, B a single part of the hoisting rope at the rear end would balance a single part of the same rope at the forward end. Similarly if the length of the jib forward of the centre of gravity L'be three times the length of the remainder, three parts of rope will be required at the rear end to balance a single part at the forward end. *This may be arranged by suitably reeving the ropes. It will be understood that the ratio between the length of the jib forward of the centre of gravity and the length of the remainder of the jib will equal the ratio between the number of partsof rope at the rear. end of the jib and the number of parts of rope at the forward end. 'The-exe amples given are merely illustrative.

Although a crane having its Jib arranged and supported as so far described with reference to Figs. 2 and 3 would operate satisfactorily there would be certain practical disadvantages. For example, the radial link H being anchored on the crane frame at J and disposed as indicated above, the crane frame (not shown) must either pass through the jib, which must be bifurcatedat its rear or lower end, or pass outside the jib, thereby requiring a bifurcated frame. V

In order to avoid these disadvantages, the ra, dial link H is replaced by its equivalent at a lower height, the length and disposition of this equivalent link 0 (Fig. 3) being as follows: Its upper end is pivoted on the crane frame at apoint P lying'on a line EJ joining the lower end E of the arm D secured to the jib A, B to the theoretically correct position J for the upper end of the radial link H, its lower end is pivoted at Qon the saidarm D towards the upper end thereof,. and its direction is such that were it extended beyondthe pivot Q it would pass through the point K- at which the radial and thrust links intersect when extended (see the dotted line QK) Although both links H andO are shown in Fig; 3 it will be understood that the link H is removed when the link 0 is fitted. Due to this modification, the crane.

frame may be shorter and not pass completely through the jib whichmay be braced on its upper side to increase its rigidity. It will'be understood that AB only represents the jib which, in practice, has an appreciable transverse dimension.

The use of the shorter equivalent link .0 entails a slight departure from the theoretically accurate horizontal movement of. the centre of gravity L of the jib A, B but, since the thrust link F does departure from theoretical accuracy which is of opposite efiect to the previous one and the two almost completely cancel out.

It should not be overlooked that the thrust link may be replaced by a straight slide and the equivalent link by an arcuate guide of a radius equal to the length of the link, although links are preferred. It may be remarked that the true theoretical level path of the centre of gravity can be ensured by the use of the slide and guide in combination.

The diagram of Fig. 4 illustrates the construction developed in the diagram of Fig. 3 applied to a jib A, B of which the centre of gravity L is disposed centrally of its length, the jib being shown in three different positions indicated by full lines, broken lines and chain-dotted lines, respectively. When the jib A, B is luffed from its full line position to its broken line position its upper extremity R moves in a curved path and rises through a vertical distance h, its centre of gravity L r'noves horizontally and its lower extremity S moves Vertically downwards also through a distance h. In the same way, when the jib is luffed from its full line position to its chain-dotted line position its upper extremity R rises vertically through a distance h and its lower extremity S falls vertically through the same distance.

Since the centre of gravity L is central of the length of the jib A, B, a single part M of hoisting rope at the upper extremity will be balanced by a single part N of the samerope at its lower extremity. Rope pulleys (not indicated in Fig. 4) are provided at R and S to take thehoisting rope which has a load hook on the end of the part M and has its part N guided over a pulley (not shown) disposed substantially vertically beneath the jib-end S, preferably atG (as assumed in Fig. 4) to run at U to a winding drum V mounted on the crane frame (not shown). It will be seen that during the lufiing movement of the jib from its full line position to its'broken line position a length hi of the part N of the hoisting rope is allowed to run upwardly over the pulley at S underthe pull of the load. It follows that the load hook T remains at the same level throughout the movement of the jib despite the rise h-of the pulley at R. Similarly, the load hook remains at the same level during the luifing move: ment to the chain-dotted position because a length 72/ of the rope-part N is paid out bythe fall of the pulley at S to compensate for the rise 71. of the pulley at R. No operation of the winding drum V is required, therefore, during the lufiing of the jib in order to keep the load hook I at the same level throughout. Nevertheless the winding drum may be operated'as desired during luinng without affecting the automatic compensation of the position of the load hook although the latter would then rise or fall in accordance with the direction of rotationof the drum.

The substantially constant horizontal velocity of the load hook T which may be required during luffing is simply ensured by arranging lufiing means such as a screw and nut (not indicated in Fig. 4) to displace the jib A, B so that its centre of gravity L moves horizontally at a constant speed. So that the crane frame may not be made too high, it is preferred not to cause the luffing means to act at the point L of the jib but to arrange them at a lower level corresponding to the attachment of the actuating screw at a point on a linejoining the centre of gravity L'Of thejib andpthe lower end E of the arm D attached tothe latter. The point of attachment of the screw should be as near'the centre ofgravity L as is permitted by practical considerations so thatthe departure from the desired constant speed ,will be very small. ,Other forms of luffing gear may, however, be'employed althoughit may then not be possible to ensure substantially constant horizontal velocity for the load hook.

It will'of course be understood 'thatthe links 'andF and arm D referred to above will normally be duplicated so that one set is disposcdlon each side of the crane frame. The hoisting'gear', slewing gear and so on do not form part of the present invention but the level lufling cranedescribed may naturally be constructed as a travelling crane adapted for slewing'if desired.

An indication of a practical form of construction of a crane corersponding to, the diagram of Fig. 4 is illustrated by Fig. 5. Here the crane frame isindicated at W as being mounted on a rotatable platform X which may be driven in any suitable manner for slewing the crane and may in turn be mounted on rails in a manner permitting of the cranes being displaced bodily. The parts of this crane which correspond to the elements of the diagram o'f Fig. 4 are indicated by the reference characters also used in that diagram; Additionally illustrated are a further pulley S. for guiding the hoisting rope '(necessitated by the shape of the jib A, B) and lufling gearcomprising a screw Y pivotally attached at Y to the link 0 and engaged in a motor-driven nut Z which is pivotally mounted at Z on the crane frame W. I

This crane operates exactly as has been described in relation to the diagram of Fig. 4,

Figs. 6 and 7 illustrate diagrammatically two further crane constructions and, where possible, corresponding parts are again indicated by like reference characters. n

The crane of Fig. 6 is arranged to haveits centre of gravity L at a distance from the pulley S of one-quarter of the length of the jib A, B,

suitable counter-weighting or loading with ballast beingresorted to, as will be understood. 'By reason of this fact a single part M'of'the hoisting rope at the upper end B ofthe jib requires three parts of the same repeat the lower endS of the jib andthis is ensured by suitably ree'ving the rope, as shown at N, before it passes at U to the drum V.

"In this example. furthermore, the luffing gear is slightly modified in its disposition by pivotally attaching the screw Y to the crane frame at Y and pivotally mounting the motor-driven nut Z on the jib A. B at a point Z lying on a linejoining the centre of gravity L to the pivot point E for the upper end of the link F.

The operation of this crane is substantially as already described above except thatthe pulley R rises vertically, during lufiing, three times as far as the pulley S sinks. This is due to the proportions chosen for the jib and still provides the necessary compensation for the load hook due to there being three parts of rope N each of which releases one-third of the total rope required.

Fig. 7 also shows a crane in which the centre of gravity, L is at a distance from the pulley S equal to one quarter of the total length of the jib A, B.. In this case, however, a further lo'ad hook T is provided, it being secured to a pulley T that is supported by two parts M, M of a hoisting rope separate from that carrying the load hook T. The part M of this rope issecured at its'upper end to the jib structure and continues around the pulley T as the part M which'runs over a pulley R. located midway betweenf'the centre of gravity L and the pulley R. The. hoisting. rope associated with-the load hook T runs from the pulley R over the pulleys S and S and extends then as three parts N of rope be tween the pulley S and the pulley mounted at G before continuing at U to the winding drum V. On the other hand, the hoisting rope associated with the load hook T runs from the pulley R to a pulley (not shown) arranged alongside the pulley S andeXten-ds then as three parts of rope between :the said pulley and another one (also not shown) arranged alongside that mounted at G before continuing at U to a second winding drum V.

In this crane the single part M of the hoisting rope for hook T balances the three parts N of this rope as in the crane of Fig. 6. In addition, as-only one (M of the parts M, M of the hoisting rope for hook T is wound, the three parts of this rope at the lower end of the jib balance the two parts M, M which are at distance from the centre of gravity L equal to one-andone-half times the distance of the pulley S from the centre'of gravity.

It will be understood that the necessary compensation is provided for both load hooks T and T during luffing of the jib by reason of this method of reeving the hoisting ropes.

Many other arrangements to suit special circumstances may be made but it is thought that the examples given will be suflicient to illustrate the invention. WhatIcl'aim is: V

'1. -A level lufiing jib crane comprising a supporting. frame, a balanced jib, a hoisting pulley atthe load-carrying end of the jib, a first countor-loading pulley at the end of the jib remote from the load, a pivot for the jib located between the said ends thereof, a second counter-loading. pulley on the-supporting frame substantially ver tically beneath the first counter-loading pulley, a winding drum on the said frame, a hoisting rope passed over said hoisting pulley and over said first and second counter-loading pulleys and attached to. the said winding drum, a first link equal in length to the distance between the jib-pivot and the first counter-loading pulley and engaged at one end with the said jib-pivot and pivotally attached at the other end to the said frame, asecond link pivotally attached at one'end to the said frame substantially vertically beneaththe said first counter-loading pulle and pivotally attached. at the other end to a point on the jib ofiset downwardly from the longitudinal axis of the jib by a distance approximately equal to the distance between the jib-pivot and the first counter-loading pulley, the said first and second links being disposed along lines meeting beneath the centre of gravity of the jib on the level of the first counter-loading pulley and the pivotal connection on the frame for the first link being vertically above the said first counter-loading pulley, and means for luffin'g the jib about its pivot and thereby displacing the said first and second links to ensure substantially horizontal movement of the centre of gravity of the jib and substantially vertical movement of the first. counter-loading pulley.

2. A crane according to claim 1, wherein the first link is replaced by an equivalent link having its one end pivoted to the crane frame at a point contained inia transverse plane that also con-'- tains both the point of attachment of the second link to the jib and the intersection of a horizontal plane passing through the centre of gravity of the jib and a transverse vertical plane containing the centre of the first counter-loading pulley, the other end of the equivalent link being pivoted'to the jib at a point located in a plane containing both the point of attachment of the said second link to the jib and the point at which the first link, if present, would be attached to the jib.

3. A level lufiing jib crane comprising a balanced jib, a" hoisting pulley at the load-carrying end of the jib, a first counter-loading pulley at the end of the jib remote from the load, a supporting frame located between the ends of the jib adjacent to that end carrying the said first counter-loading pulley, a pivot for the jib arranged between its ends, a first link pivotally attached at one end to a point on the upper end of the frame and engaged at the otherend with the jib-pivot, a second link pivotally attached at one end to the frame substantially vertically beneath the first counter-loading pulley and at the other end to the jib at a point offset from and below the longitudinal axis of the said jib, a second counter-loading pulley on the frame substantially vertically beneath the first counterloading pulley, a winding drum on the frame, a hoisting rope passed over the hoisting pulley and over the said first and second counter-loading pulleys to the winding drum, and jib-luffing means for moving the jib about the point thereon at which the said second link is attached and thus displacing the jib-pivot about the point on the frame at which the saidfirst link is attached to the latter, the said first and second links being disposed along lines that meet at the intersection of a transverse vertical plane containing the centre of gravity of the jib and a horizontal plane containing, the axisof the first counterloading pulley.

4. A level luffing jib crane as claimed in claim 3, wherein the jib-lufling means comprises luffing gear arranged to displace the centre of gravity of the jib horizontally at substantially constant speed.

5. A level lufiing jib crane as claimed in claim 3, in which the jib-lufiin means comprises screw and nut luffing gear adapted to displacethe centre of gravity of the jib horizontally at substantially constant speed.

6. A level lufiing jib crane comprising a supporting frame, a" horizontal pivot at the upper end of the said frame, a lower horizontal pivot on the said frame displaced out of the vertical plane containing the axis of the. first-mentioned pivot, a balanced jib, an integral part on the jib extending downwards from the longitudinal axis of the jib adjacent to the lower end thereof,

the pivot on the jib-part to the pivot at the upper end of the frame, when produced, passes through the intersection of a horizontal plane containing the centre of gravity of the jib and a transverse vertical plane containing the lower end of the jib, and that the two links lie on lines which meet at the intersection of a transverse vertical Plane containing the said centre of gravity and a horizontal plane containing the said lower end of the jib, a hoisting pulley at the load-carrying end of the jib, a first counter-loading pulley at the lower end of the jib, a second counter-loading pulley on the frame vertically beneath the said lower end of the jib, a winding drum on the said frame, a hoisting rope passed over the hoisting pulley and over the said first and second counterloading pulleys to the winding drum, and luffing means connected between the jib and the frame for displacing the centre of gravity of the jib horizontally at substantially constant speed.

'7. A crane as claimed in claim 6, in which the luffing means comprises screw .and nut gear.

8. A crane as claimed in claim 6, in which the first and second links are duplicated and one set is arranged at each side of the supporting frame.

9. A crane as claimed in claim 6, in which the luffing means comprises screw and nut gear pivotally attached at one end to the frame and pivotally attached at the other end to the jib at a point located on a line joining the centre of gravity of the jib to the pivot on the jib-part.

10. A crane as claimed in claim 6, including a further hoisting pulley intermediate the ends of the jib, a second winding drum on the frame, duplicate first and second counter-loadin pulleys on the lower end of the jib and on the frame, respectively, and a second hoisting rope passed over the said further hoisting pulley and over 40 the said duplicate first and second counter-loada horizontal pivot on the lower end of the jibpart spaced from .the intersection of the medial line of the said part with the said axis by'a distance substantially equal to that between the said intersection and the lower end of the jib, a horizontal jib-pivot located on the said medial line, a first link extending between the pivot at the upper end of the frame and the said jibpivot, a second link extending between the lower pivot on the said frame and the pivot on'the said jib-part, the said first and second links being of such lengths and so disposed that the lower end of the jib is substantially vertically above the said lower pivot, that a line joining ing pulleys to the said second winding drum.

11, In a crane as claimed in claim 6, mounting the supporting frame slewably on a travelling base structure.

12. A level lufling jib crane comprising a supporting frame, a balanced jib, a hoisting pulley at the load-carrying end of the jib, a first counter-loading pulley at the end of the jib remote from the load, a pivot for the jib located between the said ends thereof, a second counter-loading pulley on the supporting frame substantially vertically beneath the first counter-loading pulley, a winding drum on the said frame, a hoisting rope passed over said hoisting pulley and over said first and second counter-loading pulleys and attached to th said Winding drum, means mounting the jib-pivot on the said frame for arcuate movement about a point thereon, a rigid part on the jib extending at an angle downwards away from the longitudinal axis of the jib with its upper end in the neighbourhood of the jib-pivot and its lower end spaced from the said jib-pivot by approximately the distance between the latter and the first counter-loading pulley, means connecting the lower end of the said jib-part to the frame for movement substantially along a line joining the said lower end and the point on the frame about which the jib-pivot moves, and means for luifing the jib and thereby simultaneously producing displacement of both the jibpivot and the lower end of the said jib-part So that the centre of gravity of the jib moves horizontally and the first counter-loadin pulley moves vertically. Y

IGNATIUS KAY. 

